FIGS. 1A˜1D are schematic views illustrating a conventional pressure sensor and a display module with the pressure sensor. The pressure sensor is disclosed in U.S. Pat. No. 8,669,952.
As shown in FIG. 1A, the pressure sensor 100 comprises a sealed chamber 102, a top surface 104, a first electrode 106, a second electrode 108 and a bottom surface 118. An elastic polymer medium 110 with distributed metallic nanoparticles 112 is filled in the sealed chamber 102. The first electrode 106 is formed on the top surface 104. The second electrode 108 is formed on the bottom surface 118. Moreover, the first electrode 106 and the second electrode 108 are transparent electrodes such as indium tin oxide (ITO) electrodes.
Please refer to FIG. 1B. In response to an applied pressure 116 on the top surface 104, the distance between the first electrode 106 and the second electrode 108 is decreased and the elastic polymer medium 110 is compressed. That is, the distance between the metallic nanoparticles 112 is changed in response to an applied pressure 116 on the top surface 104. As the applied pressure is increased, the distance between the metallic nanoparticles 112 is decreased. Consequently, the electrical resistance between the first electrode 106 and the second electrode 108 is decreased.
In case that no pressure is applied to the pressure sensor 100 (see FIG. 1A), the electrical resistance between the first electrode 106 and the second electrode 108 is R1. In case that the pressure 116 is applied to the pressure sensor 100 (see FIG. 1B), the electrical resistance between the first electrode 106 and the second electrode 108 is R2, wherein R1>R2.
FIG. 1C is a schematic top view illustrating a display module with the pressure sensor. FIG. 1D is a schematic cross-sectional view illustrating the display module of FIG. 1C and taken along the line 2B. The display module 200 comprises a front panel 201 with an array of display pixels 202, a backlight panel 204 underlying the front panel 201, and a touchscreen 206 overlying the front panel 201. The touchscreen 206 comprises an array of pressure sensor cells 100. The pressure sensor cell 100mn is also referred as a sensing node.
Generally, each of the pressure sensor cells 100 has the structure as shown in FIG. 1A. Take the pressure sensor cell 100mn as an example. The pressure sensor cell 100mn comprises a sealed chamber, a top surface, a first electrode 106n, a second electrode 108a and a bottom surface. As shown in FIG. 10, the relationship between the input and the output can be used to judge which pressure sensor cell receives the applied pressure. Moreover, the magnitude of the pressure applied to the pressure sensor cell can be determined according to the electrical resistance between a first electrode and a second electrode.
FIGS. 2A˜2D are schematic views illustrating a conventional pressure-sensitive cell. The pressure-sensitive cell is disclosed in U.S. Pat. No. 8,736,574.
As shown in FIG. 2A, a matrix 300 comprises plural pressure-sensitive cells. The electrical resistance of the pressure-sensitive cell is changed according to the amount of force applied thereto. Generally, the electrical resistance of the pressure-sensitive cell is in reverse proportion to the amount of force applied thereto.
The matrix 300 has a first layer 322 including plural column conductors 324. The matrix 300 also has a second layer 326 including plural row conductors 328. The second layer 326 is made of a flexible material. When a force is applied to the second layer 326, the second layer 326 is temporarily subjected to deformation.
As shown in FIG. 2B, each intersection of a column conductor 324 on the first layer 322 and a row conductor 328 on the second layer 326 establishes a pressure-sensitive cell 336. The pressure-sensitive cell 336 further comprises a force-sensitive resistive material 338. The column conductor 324 and the row conductor 328 are covered by the force-sensitive resistive material 338.
Generally, if no force is applied to the pressure-sensitive cell 336, the force-sensitive resistive material 338 on the column conductor 324 and the force-sensitive resistive material 338 on the row conductor 328 are not in contact with each other. If the force applied to the pressure-sensitive cell 336 exceeds a smallest threshold force, the force-sensitive resistive material 338 on the column conductor 324 and the force-sensitive resistive material 338 on the row conductor 328 are in contact with each other.
For achieving the above purposes, as shown in FIG. 2C, the pressure-sensitive cell 336 further comprises islands 374 and lands 375. The islands 374 and the lands 375 are disposed on the first layer 322 and the second layer 326, respectively. Moreover, the column conductors 324 and the row conductors 328 are electrically isolated by spacers 344. Consequently, if no force is applied to the pressure-sensitive cell 336, the force-sensitive resistive material 338 on the column conductor 324 and the force-sensitive resistive material 338 on the row conductor 328 are not in contact with each other.
The pressure-sensitive cell 336 further comprises a force-spreading layer 346. The force-spreading layer 346 is used for diffusing the force of the touch input to two or more pressure-sensitive cells within matrix 320. The force-spreading layer 346 comprises bumps 348. The bumps 348 are in contact with the second layer 326. Consequently, when a force is applied to the force-spreading layer 346, the force is transferred to the second layer 326 through the bump 348. The force-spreading layer 346 further comprises troughs 78. The troughs 78 are arranged between the bumps and aligned with the corresponding islands 374 and the corresponding lands 375.
Please refer to FIG. 2D. When a force is applied to a contact area 350 of the matrix 320, the force-spreading layer 346 is subjected to deformation. Consequently, the bumps 348 and 347 are in contact with the second layer 325, and the force is transferred to the pressure-sensitive cells 352, 353 and 354 of the matrix 320. Under this circumstance, the force-sensitive resistive material 338 on the second layer 326 and the force-sensitive resistive material 338 on the first layer 322 at the locations 356, 357 and 358 of the pressure-sensitive cells 352, 353 and 354 are in contact with each other. Consequently, the electrical resistances of the pressure-sensitive cells 352, 353 and 354 are decreased. Moreover, since the islands 374 and the lands 375 are separated from each other by the spacers 344, the force-sensitive resistive material 338 on the second layer 326 and the force-sensitive resistive material 338 on the first layer 322 at the locations corresponding to the islands 374 and the lands 375 are not in contact with each other.
From the above discussions, the conventional pressure sensors are disposed over a LCD display module, or disposed over an AMOLED display module, or installed in an outer frame of the display module, or integrated into the LCD pixels. However, regardless of the configurations of the pressure sensors, the pressure sensors are disposed over the backlight panel. In such configuration, the illuminance of the display module is reduced. Moreover, since the structures of the conventional pressure sensors are complicated, the process yield of the display module is impaired.